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Extreme tyre-road mu values under certain conditions
(33 posts, started )
#26 - axus
Just one more question - and a complex one at that. We can get the traction budget for each tyre drawn based on all the infromation you have given us but from there it will get difficult as we need to estimate the traction budget of the whole car based on that. Any ideas?
Are you just using a 'rolling raod' scenario for your example or are you trying to incorporate a dynamic situation including power output through the vehicle and cornering etc?

If it is a recognised standard of unit (It might be, I don't know) then just add the values for each tyre until you reach a total. More than likely to get a whole picture for all four tyres you might have to factor in an equation to take into account the vehicle. So four * tyre value / by vehicle weight or something like that. Having spoken to some engineers about stuff similar the actual physics behind all this is very very very very compicated. As is the maths. What I think you are trying to nobel-ly do is condense a huge amount of information and science into a simple model for us lay people. Hats of gents. I hope it works out for you.
#28 - axus
Well I have been thinking about it and think people might need to input part of their setup so that the sprung mass on each wheel can be calculated based on the body roll and then that will give you the mass each tyre is accelerating. Then you will have to find the force based on F = m*a (a being the mu for that tyre under that body roll). How you will work out the total acceleration from there is something that I cannot figure out. I will speak to people who may know about this but this will be one of the more difficult tasks. EDIT: I think I figured a solution out with the help of my brother - we will have a to calculate the forces exerted by the tyres onto the road for every combination of roll, pitch and usage the entire traction budget for each tyre in a different directions. Obviously the body roll will have to be opposite to the direction in which you are turning and all the forces will have to be in the same quadrant (ie. 0-90deg, 90-180deg, 180-270deg and 270-360deg). It should give a pretty good estimate. Any better suggestions are welcome though.
{I know this thread is old, but it's referenced by the current version of LRA, so...}

Nobody seems to have quibbled about whether 1/4 of the unsprung mass is the right correction to use for the lumps of "stuff" hanging off the suspension.
I'm wondering though if it wouldn't be quite different at the front and back? For many cars (FZR and BF1 are just two examples) the front and rear tyres seem very different in size, and probably the hubs and brake units might have rather different mass too. So we might be seriously underestimating the unsprung mass at the rear of the car, and overestimating at the front?
#30 - w126
Using the data from CAR info binary format is for sure better than 1/4 of unsprung mass. FWIR exporting of it was added in LFS later than the discussion in this thread took place.
Aha - cool, thanks. Hadn't spotted that!

Update: just had a peek at the BF1 bin file. If I parsed it right, the rears have unsprung mass of 21.06 (kilograms I guess?) and the fronts have 19.67. Much more similar than I'd have guessed!
Currently only the wheels and tyres contribute to unsprung mass - brakes and suspension components do not. Whenever this gets added, it will no doubt affect the difference between front and rear unsprung masses.
Ah... And I was just thinking that the brakes might actually be the reason why the gap was so small! (The front brakes being so much meatier than the rears...)

Extreme tyre-road mu values under certain conditions
(33 posts, started )